804 



THE OEGANS OF SENSE. 



the openings of the anterior ethmoidal cells, and, in rather more than fifty per cent 

 of skulls, is continued upwards as the fronto-nasal duct into the frontal air-sinus ; 

 in the remainder it is shut off from the lower end of the fronto-nasal duct by 

 the union of the anterior part of the bulla ethmoidalis with the upper end of 

 the processus uncinatus, and the fronto-nasal duct then opens into the anterior 

 part of the middle meatus. The ostium maxillare or opening of the maxillary sinus 

 is placed below the bulla ethmoidalis, and is hidden by the lower end of the 

 processus uncinatus ; an accessory ostium is frequently seen in the middle meatus, 

 above the posterior part of the inferior nasal concha. 



The inferior meatus lies below the inferior nasal concha, under cover of the 

 anterior part of which is the slit-like orifice of the naso-lacrimal duct (see p. 825). 



The roof is very narrow, except at its posterior part, and is divisible into three 

 portions, fronto-nasal, ethmoidal, and sphenoidal, in accordance with the bones 

 which enter into its formation. 



The floor is nearly horizontal from before backwards, and is formed by the 

 palatine process of the maxilla and the horizontal part of the palatine bone. In 

 it, close to the inferior margin of the septum and immediately over the incisive 

 foramen, a slight depression, the naso-palatine recess, is sometimes seen ; it is directed 

 downwards and forwards for a short distance, and indicates the position of a 

 communication which existed between the nasal and buccal cavities in early 

 foetal life. 



Membrana Mucosa Nasi. The nasal mucous membrane is thick, highly 

 vascular, and firmly bound to the subjacent periosteum and perichondrium. It 

 is continuous, through the choanae, with the mucous lining of the nasal part of the 

 pharynx; through the naso-lacrimal and lacrimal ducts, with the conjunctiva; 

 and, through the apertures leading into the air-sinuses, with the delicate lining 

 of these cavities. 



Throughout the respiratory region it is covered with columnar, ciliated 

 epithelium, interspersed amongst which are goblet or mucin cells, whilst between 

 the bases of the columnar cells smaller pyramidal cells are interpolated. It contains 

 a freely anastomosing venous plexus, which in some parts, e.g. over the inferior nasal 

 conchse, forms a cavernous plexus. Many acinous glands, secreting a watery fluid, 

 are embedded in it, and are especially large and numerous in the posterior halves of 



the nasal cavities, 



Zone of oval 

 nuclei 



Zone of 



round nuclei 



Basal cells 



Olfactory 

 glands 



I Epithelium 



_ tory glands 



FIG. 675. SECTION THROUGH THE OLFACTORY Mucous MEMBRANE. 



while in children 

 the mucous 



membrane con- 

 Duct of one , . . i 



oftheoifac- tains a consider- 

 able amount of 

 adenoid tissue. 



In the olfac- 

 tory region the 

 mucous mem- 

 brane is yellow- 

 ish in colour, 

 more delicate, 

 and is covered 

 with non-ciliated 

 columnar epi- 

 thelium (Figs. 

 675, 676). Em- 

 bedded in it are 

 numerous tubu- 

 lar and branched 



glands, the olfactory glands, which are lined with polygonal cells and open by fine 

 ducts on its free surface. The epithelium of the olfactory region consists of : (1) 

 supporting cells, (2) olfactory cells, and (3) basal cells. 



1. Supporting Cells. The superficial parts of these cells are columnar in shape 

 and contain fine granules of yellow pigment, whilst the deeper portions are continued 



